(1) Field of the Invention
The present invention relates to an apparatus and method for guiding a vehicle occupant to travel from a present position to a set destination to which the vehicle occupant desires to reach using a display unit.
(2) Description of the Background Art
Various types of vehicular route guidance apparatuses have been proposed in which an optimum route from a present position of the vehicle to a destination is searched and the optimum route is displayed together with the present position of the vehicle on a road map image of a display unit screen so as to conveniently guide the vehicle occupant toward the destination.
The optimum route to the destination is searched from an infinite number of routes to the destination formed by retrieving tremendous amounts off intersection network data so that the optimum route is selected as, for example, a running distance of travel is shortest or a required running time of travel is shortest.
Since, however, in the various types of the guidance apparatuses described above, the search of the optimum route is started upon the setting of the destination, the vehicle driver or vehicle occupant needs to wait for the end of the search in order to receive the result of vehicle route guidance to the destination.
To solve such disadvantages as described above, a Japanese Patent Application First Publication No. Heisei 2-184998 exemplifies an improvement in a special search algorithm to shorten a time it takes to search for the optimum route. A Japanese Patent Application First Publication No. Heisei 2-306400 exemplifies a limitation on an area in a road map to be searched to similarly shorten the optimum route search time. In addition, a Japanese Patent Application First Publication No. Heisei 2-56591 exemplifies a hierarchy structure in the intersection network data to similarly shorten the optimum route search time. However, it requires much time for the search for the optimum route for several minutes upon the setting of the destination even when either of the above-described route search techniques disclosed in the above-identified Japanese Patent Application First Publications is used.